The present invention relates to an acoustic touch position sensor, and more particularly to such a sensor wherein a coordinate position, and optionally an absorption characteristic, of an acoustic disturbance is determined by analyzing a plurality of received signals. The present invention allows the sensing system to employ waves to differ in path geometry, and/or wave characteristic type, e.g., mode, frequency, waveform, velocity, and/or wavelength. This system advantageously allows redundant position measurement and/or differential wave perturbation sensing.
Acoustic touch position sensors are well known. A common system includes two sets of transducers, each set having a different axis aligned respectively with the axes of a physical Cartesian coordinate system defined by a substrate. An acoustic pulse is generated by one transducer, propagating as a Rayleigh wave along an axis which intersects an array of reflective elements, each element angled at 45xc2x0 and spaced corresponding to an integral number of wavelengths of the acoustic wave pulse. Each reflective element reflects a portion of the wave along a path perpendicular to the axis, across an active region of the substrate, to an opposing array and transducer which is a mirror image of the first array and transducer. The transducer in the mirror image array receives an acoustic wave consisting of superposed portions of the wave reflected by the reflective elements of both arrays, directed antiparallel to the emitted pulse. Wavepaths in the active region of the sensor have characteristic time delays, and therefore a wavepath or wavepaths attenuated by an object touching the active region may be identified by determining a timing of an attenuation in the composite returning waveform. A second set of arrays and transducers are provided at right angles to the first, and operate similarly. Since the axis of a transducer corresponds to a physical coordinate axis of the substrate, the timing of an attenuation in the returning wave is indicative of a Cartesian coordinate of a position on the substrate, and the coordinates are determined sequentially to determine the two dimensional Cartesian coordinate position of the attenuating object.
The applicability of such systems as commonly employed is restricted by the following major limitations. First, acoustically absorptive contamination in localized regions, e.g. a water drop on a known Rayleigh-wave sensor, result in large areas of shadowing in which two-dimensional touch positions cannot be reconstructed. Second, the configurational requirements of these sensors limits their versatility with regard to shape and size. Third, reconstruction of touch coordinates may lead to ambiguities when more than one touch is applied simultaneously. Finally, such sensors provide limited touch characteristic information from which to differentiate valid touches from false touches, e.g. fingers from water drops. The present invention addresses these problems.
Present commercial touch screen products generally serve applications in which the touchscreen is an input device that is intended to be used by one user at a time. An automatic-teller-machine (ATM) banking application is typical. While many customers may sequentially use a touchscreen based automatic teller machine, each user in turn has a private dialog with the system. In contrast, few if any touchscreen products are presently available for applications in which the touchscreen is an input device that is intended to be used by more than one user simultaneously.
a. Parallel Transducer Arrays
Acoustic touch position sensors are known to include a touch panel or plate having an array of transmitters positioned along a first edge of a substrate for simultaneously generating parallel surface acoustic waves that directionally propagate through the panel to a corresponding array of detectors positioned opposite the first array on a second edge of the substrate. Another pair of transducer arrays is provided at right angles to the first set. Touching the panel at a point causes an attenuation of the waves passing through the point of touch, thus allowing interpretation of an output from the two sets of transducer arrays to indicate the coordinates of the touch. This type of acoustic touch position sensor is shown in U.S. Pat. No. 3,673,327 and WO 94/02911, Toda, incorporated herein by reference. By employing a direct acoustic path from a transmitting transducer to a corresponding receiving transducer, an acoustic path length which is approximately equal to the height or width of the substrate is provided, as shown in FIG. 1. Because the acoustic wave diverges, a portion of a wave emitted from one transmitting transducer will be incident on a set of receiving transducers, as shown in FIG. 2.
b. Reflective Arrays
In order to reduce the number of transducers required for an acoustic touchscreen, Adler, Re. 33,151, and U.S. Pat. No. 4,700,176, provide a reflective array for reflecting portions of an acoustic wave along incrementally varying paths. Therefore, if two such arrays are disposed opposite one another, as shown in FIG. 4, a single transmit and receive transducer will allow touch sensing along one axis of the substrate, with a maximum acoustic path length of twice the height plus width or twice the width plus height of the touch sensitive area. The maximum acoustic path length is a useful metric for acoustic touch sensors because most materials, e.g., glass, have a relatively constant acoustic power loss expressed in dB per unit length; the greater the path length, the greater the attenuation. In many cases, it is this attenuation of the acoustic signal which limits the design of the touchscreen, and therefore it is generally desired to have high acoustic efficiency in each of the touchscreen components to allow design leeway. Thus, for example, greater numbers of transducers may be selectively deployed to allow larger substrates, and likewise, with limited size substrates, acoustic paths may be folded to reduce a required number of transducers.
In order to provide a set of surface acoustic waves which propagate across a broad region of the substrate in parallel, an acoustically reflective grating having elements set at 45xc2x0 to the axis of the beam is disposed along its path, each element reflecting portions of the wave at right angles to the axis of propagation. The acoustic waves are then collected, while maintaining the time dispersion information which characterizes the axial position from which an attenuated wave originated. The position of a touch in the active area is thus determined by, e.g., providing another reflective grating opposite the first, which directs the surface acoustic waves as a superposed wave to another transducer along an antiparallel path, recording the time of arrival and amplitude of a wave pattern, an attenuation of which corresponds to a touch and a characteristic time corresponding to a position along the axis of the arrays. The touch, in this case, may include a finger or stylus pressing against the surface directly or indirectly through a cover sheet. See, e.g., U.S. Pat. No. 5,451,723. In addition, if the emitted wave diverges, one of the reflective arrays may be eliminated, as shown in FIG. 3, although a rectangular coordinate system is not provided. In the case shown in FIG. 3, the maximum path length is approximately the height plus the width. Acoustic touch position sensors are also known wherein a single transducer per axis is provided for emitting a surface acoustic wave, as shown in FIG. 5. In this case, the maximum path length is two times the sum of the height plus width.
The known reflective arrays are generally formed of a glass frit which is silk-screened onto a soda-lime glass sheet formed by a float process, and cured in an oven to form a chevron pattern of raised glass interruptions. These interruptions typically have heights or depths of order 1% of the acoustic wavelength, and therefore only partially reflect the acoustic energy.
Thus, with waves having surface energy, the reflecting arrays may be formed on the surface, and where wave energy is present on both sides of the substrate, these reflecting arrays may be formed on one or both sides of the substrate. Because the touch sensor is generally placed in front of a display device, and because the reflective array is generally optically visible, the reflective arrays are generally placed at the periphery of the substrate, outside of the active sensing area, and are hidden and protected under a bezel. The reflective elements of the reflective array each generally reflect of order 1% of the surface acoustic wave power, dissipating a small amount and allowing the remainder to pass along the axis of the array. Thus, array elements closer to the transmitting transducer will be subject to greater incident acoustic energy and will therefore reflect a greater amount of acoustic power. In order to provide equalized acoustic power at the receiving transducer, the spacing of the reflective elements may be decreased with increasing distance from the transmitting transducer, or the acoustic reflectivity of the reflective elements may be altered, allowing increased reflectivity with increasing distance from the transmitting transducer.
Adler, U.S. Re. 33,151, relates to a touch-sensitive system for determining a position of a touch along an axis on a surface. A surface acoustic wave generator is coupled to a sheet-like substrate to generate a burst of waves, which are deflected into an active region of the system by an array of wave redirecting gratings. According to a disclosed example, surface acoustic waves traversing the active region are, in turn, redirected along an axis by gratings to a receiving transducer. A location of touch is determined by analyzing a selective attenuation of the received waveform in the time domain, each characteristic delay corresponding to a locus on the surface. The redirecting gratings are oriented at 45xc2x0 to the axis of propagation, and spaced at integral multiples of the surface acoustic wave wavelength, with dropped elements to produce an approximately constant surface acoustic wave power density over the active area. The spacing between grates decreases with increasing distance along the axis of propagation from the transducer, with a minimum spacing of at least one wavelength of the transmitted wave. U.S. Pat. Nos. 5,329,070, 5,260,521, 5,234,148, 5,177,327, 5,162,618 and 5,072,427 propose specific examples of types of surface acoustic waves that may be used in the acoustic sensor system taught in the Adler patents.
Where a separate reflective array is provided to redirect acoustic waves toward the receiving transducer, these are also provided with an increasing acoustic reflectivity with increasing distance from the receiving transducer. This is to reduce signal loss with propagation of the signal toward the receiving transducer along the axis of the reflective array. Typically, array pairs are designed as mirror images of one another.
U.S. Pat. No. 4,642,423, to Adler, incorporated herein by reference, addresses pseudo-planarization techniques for rectangular touchscreen surfaces formed by small solid angle sections of a sphere. According to Adler, reflective elements are angled to excite waves along sections of great circles of the spherical surface which extrapolate to a common intersection point. This patent addresses the need for touchscreens that match the curvature of CRT faceplates, for which the radius of curvature is always large compared to the diagonal dimension of the faceplate. This patent teaches means to minimize the inherent differences between spherical geometry of a small portion of a sphere and the Cartesian plane, allowing use in conjunction with controllers that are designed for flat sensor geometry. The acoustic waves generated by the system of Adler are substantially orthogonal. Known embodiments of the Adler technology include 19 inch diagonal CRTs with a radius of curvature of 32 inches and 13 or 14 inch diagonal CRTs with a radius of curvature of 22.6 inches.
c. Two Dimensional Position Sensing
In order to receive information determinative of the coordinates of a touch, two acoustic waves, each propagating across the active region of the substrate along perpendicular axes are provided. Thus, the two axes are typically used in conjunction to recognize a valid touch, but may also be analyzed separately and non-interactively to sequentially determine a position along each of the two orthogonal coordinate axes. In these known systems, the coordinate axes of interest to the application are defined by the physical configuration of the sensor. Thus, sensor design is constrained by the requirements of the application""s coordinate system.
In known systems, the system operates on the principle that a touch on the surface attenuates surface acoustic waves having a power density at the surface. An attenuation of a wave traveling across the substrate causes a corresponding attenuation of waves impinging on the receive transducer at a characteristic time period. Thus, the controller need only detect the temporal characteristics of an attenuation to determine the axial coordinate position. Measurements are taken along two axes sequentially in order to determine a Cartesian coordinate position.
Other known systems, described in more detail below, employ a single reflective array for separating as a plurality of wave paths, and superposing as a composite waveform, the signal from the transducer, through the active region, along a plurality of paths and then back to the transducer, by providing an acoustically reflective edge spaced parallel to the reflective array, causing the dispersed wave to traverse the active region twice, as shown in FIG. 5. See, U.S. Pat. No. 5,177,327, FIG. 10 and accompanying text, incorporated herein by reference.
FIG. 11 of U.S. Pat. No. 4,700,176 teaches the use of a single transducer for both transmitting the wave and receiving the sensing wave, with a single reflective array employed to disperse and recombine the wave. Such systems therefore employ a reflective structure opposite the reflective array. As a result, an acoustic wave passes through the active region twice, with consequent increased wave absorption by the touch but also increased overall signal attenuation due to the reflection and additional pass through the active region of the substrate. Thus, the acoustic wave may be reflected off an edge of the substrate or an array of 180xc2x0 reflectors parallel to the axis of the transmission reflective grating and reflected back through the substrate to the reflective array and retrace its path back to the transducer. The transducer, in this case, is time division multiplexed to act as transmitter and receiver, respectively, at appropriate time periods. A second transducer, reflective array and reflective edge are provided for an axis at right angles to allow determination of a coordinate of touch along perpendicular axes.
A known system by Electro-Plasma (Milbury Ohio) employs a bisected reflecting array in order to reduce an acoustic wavepath, as shown in FIG. 6A. Therefore, a maximum path length of an acoustic wave along the composite reflecting array from a transducer is about one half of the total width, with transducers each sending acoustic waves toward the bisection point. Thus, the orthogonal set of paths will be longer, with a maximum total path length of two times the height plus the width. In this system, transmitting transducers are excited individually and produce identical types of waves, portions of which travel along parallel paths, with a small overlap of acoustic wave coverage of the touchscreen in order to avoid a dead zone in the touch region. The acoustic waves follow the traditional paths corresponding to axes parallel to the Cartesian coordinate axes. A similar type system would bisect both sets of reflective arrays, as shown in FIG. 6B.
The xe2x80x9ctriple transitxe2x80x9d system, shown in FIG. 8, provides for a single transducer which produces a sensing wave for detecting touch on two orthogonal axes, which both produces and receives the wave from both axes. In this case, the area in which touch is to be sensed is generally oblong, such that the longest characteristic delay along one path is shorter than the shortest characteristic delay along the second path, thereby allowing differentiation between the two axes based on time of reception. See, U.S. Pat. Nos. 5,072,427, 5,162,618, and 5,177,327, incorporated herein by reference. The maximum path length of the triple transit design is four times the width plus two times the height. Due to the significant difference in path lengths, the X and Y signals are non-overlapping, as shown in FIG. 9C.
d. Controller Algorithms
The wave pattern of one type of known acoustic touch sensors is dispersed along the axis of the transmitting reflective array, traverses the substrate and is recombined, e.g., by another reflective grating, into an axially propagating wave, dispersed in time according to the path taken across the substrate, and is directed to a receiving transducer in a direction antiparallel to the transmitted wave, which receives the wave and converts it into an electrical signal for processing based on signal amplitude received as a function of time. Thus, according to this system, only two transducers per axis are required. Because of the antiparallel path, the time delay of a perturbation of the electrical signal corresponds to a distance traveled by the wave, which in turn is related to the axial distance from the transducer along the reflecting arrays traveled by the wave before entering the active area of the substrate, i.e., approximately two times the distance along the axis of the array plus the spacing between the arrays. A typical set of return waveforms is shown in FIG. 9.
The location of a touch is determined by detecting an attenuation of the received signal amplitude either in absolute terms or as compared to a standard or reference received waveform. Thus, for each axis, a distance may be determined, and with two orthogonal axes, a unique coordinate for the attenuation determined. Acoustic touch position sensors of this type are shown in U.S. Pat. Nos. 4,642,423, 4,644,100, 4,645,870, 4,700,176, 4,746,914 and 4,791,416, incorporated herein by reference.
U.S. Pat. Nos. Re. 33,151, and 4,700,176 also disclose a touch sensor system having a set of diverging acoustic paths which are incident on a reflective array having elements located along an arc and spaced to meet coherency criteria. See, Re. 33,151, and 4,700,176, FIG. 16 and accompanying text, incorporated herein by reference. This touch sensor produces a unidimensional output which corresponds to an angular position of a touch.
According to known systems, a number of algorithms are employed to determine the coordinate position of a touch. The simplest algorithm is a threshold detection, in which an amplitude of a received signal is compared to a set value. Any dip below that value is considered indicative of a touch. More sophisticated is an adaptive threshold, in which the threshold varies based on actual sets of received data, thus allowing increased sensitivity and rejection of artifacts of limited amplitude.
A control circuit may operate in a number of modes, e.g., number of transducers and configuration. In known systems having a rectangular substrate without redundancy, the number of transducers varies: 1 (triple transit); 2 (ExZec/Carroll Touch); 4 (Adler); and 6 (ElectroPlasma). There is a natural 8 transducer arrangement, not present in prior art designs, which is an extension of 6 transducer scheme in which 4 transducers are used for both X and Y axis measurements; see FIG. 6B.
Known systems also include an adaptive baseline, in which an amplitude of the normal received signal over time is stored, and the received signal is compared to a baseline having a characteristic timeframe. In this system, an artifact in one position does not necessarily reduce sensitivity at another.
Brenner et al., U.S. Pat. No. 4,644,100 relates to a touch sensitive system employing surface acoustic waves, responsive to both the location and magnitude of a perturbation of the surface acoustic waves. The system according to U.S. Pat. No. 4,644,100 is similar in execution to the system according to US Re. 33,151, while determining an amplitude of a received wave and comparing it to a stored reference profile.
In order to reduce the number of transducers, the known xe2x80x9ctriple transitxe2x80x9d system reflects the acoustic signal so that a wave emitted by a single transducer is dispersed as parallel waves along a first axis, then reflected at a right angle and dispersed as parallel waves along a second axis. These waves are then reflected back to the arrays and then back to the transducer, so that all the waves traveling along the first axis are received by the transducer prior to any waves traveling along the second axis, generally requiring an oblong substrate. The controller therefore sets two non-overlapping time windows for the received signal, a first window for the first axis and a second window for the second axis. Therefore, each time window is analyzed conventionally, and the pair of Cartesian coordinates is resolved.
A system for sensing a force of a stylus against an acoustic touch-sensitive substrate is disclosed in U.S. Pat. No. 5,451,723, incorporated herein by reference. This system converts the point-contact of the rigid stylus portion into an area contact of an acoustically absorptive elastomer, placed between the stylus and the substrate.
e. Wave Modes
xe2x80x9cSurface acoustic wavesxe2x80x9d (xe2x80x9cSAWxe2x80x9d), as used herein refers to acoustic waves for which a touch on the surface leads to a measurable attenuation of acoustic energy. Several examples of surface acoustic waves are known.
The vast majority of present commercial products are based on Rayleigh waves. Rayleigh waves maintain a useful power density at the touch surface due to the fact that they are bound to the touch surface. Mathematically, Rayleigh waves exist only in semi-infinite media. In practice it is sufficient for the substrate to be 3 or 4 wavelengths in thickness. In this case one has quasi-Rayleigh waves that are practical equivalents to Rayleigh waves. In this context, it is understood that Rayleigh waves exist only in theory and therefore a reference thereto indicates a quasi-Rayleigh wave.
Like Rayleigh waves, Love waves are xe2x80x9csurface-bound wavesxe2x80x9d. Particle motion is vertical and longitudinal for Rayleigh waves. Both shear and pressure/tension stresses are associated with Rayleigh waves. In contrast, particle motion is horizontal, i.e. parallel to touch surface, for Love waves. Only shear stress is associated with a Love wave. Other surface-bound waves are known.
Another class of surface acoustic waves of possible interest in connection with acoustic touchscreens are plate waves. Unlike surface-bound waves, plate waves require the confining effects of both the top and bottom surfaces of the substrate to maintain a useful power density at the touch surface. Examples of plate waves include symmetric and anti-symmetric Lamb waves, zeroth order horizontally polarized shear (ZOHPS) waves, and higher order horizontally polarized shear (HOHPS) waves.
The choice of acoustic mode affects touch sensitivity, the relative touch sensitivity between water drops and finger touches, as well as a number of sensor design details. However, the basic principles of acoustic touchscreen operation are largely independent of the choice of acoustic mode.
f. Optimization for Environmental Conditions
The exposed surface of a touchscreen is ordinarily glass. While certain systems may include such additions, electrically conductive coatings or cover sheets are not necessary. Therefore, acoustic touchscreens are particularly attractive for applications which depend on public access to a durable touch interface.
Semi-outdoor applications, e.g., ATMs, ticket booths, etc., are of particular interest. Typically in such applications, the touchscreen is protected from direct environmental precipitation contact by a booth or overhang. However, indirect water contact, due to user transfer or condensation is possible. Thus, users coming out of the rain or snow with wet clothes, gloves or umbrellas are likely to leave occasional drops of water on the touchscreen surface. Water droplets have a high absorption of Rayleigh waves in known systems; thus, a drop of water in the active region will shadow the acoustic paths intersecting that drop, preventing normal detection of a touch along those axes.
One approach to limit water contact with the touchscreen surface is to employ a cover sheet. See U.S. Pat. No. 5,451,723. However, a cover sheet generally reduces the optical quality of the displayed image seen through the resulting sensor and leads to a less durable exposed surface. Another approach to reducing the effects of water droplets is to employ a wave mode which is less affected by the droplets, such as a low frequency Rayleigh wave, see U.S. Pat. No. 5,334,805, a Lamb wave, see U.S. Pat. Nos. 5,072,427 and 5,162,618, or a zero order horizontally polarized shear wave, see U.S. Pat. No. 5,260,521. These waves, however, also have reduced sensitivity, resulting in either reduced touch sensitivity of the touch system, increased susceptibility to electromagnetic interference, or more expensive controller circuitry.
In the case of Rayleigh waves, a lower frequency operation requires a thicker substrate, e.g., 3 to 4 wavelengths of the wave, and wider reflective arrays and transducers. The increased bulk of a sensor designed for low-frequency Rayleigh waves is typically a serious mechanical design problem. In the case of Lamb waves, a thin substrate is required, e.g., about 1 mm at about 5 MHz. These thin substrates are fragile, and Lamb waves have energy on both top and bottom surfaces, making optical bonding problematic due to signal damping. In the case of a ZOHPS wave, in contrast to a Rayleigh wave, the relative sensitivity is greater to a finger than to water droplets. Further, ZOHPS waves support limited options for optical bonding, such as RTVs (silicone rubbers) which do not support shear radiation damping.
Shear sensors have two disadvantages in cold climates. In particularly cold climates, it is important for touchscreens to sense touches of fingers of gloved hands. Shear waves have reduced sensitivity compared to Rayleigh waves thus making detection of gloved fingers more difficult. Secondly, in such climates, drops of water may freeze to form solid ice. While liquid water does not strongly couple to horizontally polarized shear waves, ice does. Thus drops of water which freeze on the touchscreen surface will cause shadowing or blinding.
There remains a need for a touch position sensor which operates reliably in the increasingly rugged environments to which such devices are deployed. There thus exists a need to supplement existing technologies in order to extend the applicability of acoustic touch sensor systems.
g. Size Constraints.
Acoustic sensors of the Adler type have been considered for use in electronic white boards; see FIG. 10 and associated text in E.P. Application 94119257.7, Seiko Epson. At present, no commercial electronic whiteboard products are available based on acoustic sensors technology. In part, this is because of size limitations for known acoustic technology.
The present invention derives from an understanding that acoustic position measurement technology suffers from various limitations, which may be addressed by implementing a system with various forms of partial redundancy in the sensing waves. Thus, for each coordinate axis of the output, a plurality of sets of waves are provided bearing information about the position of a single touch along that axis. Therefore, any limitation in the ability of one set of waves to determine a touch position may be supplemented by information derived from at least one other set of waves. Because the redundancy may be partial, other information may be derived from the available sets of waves as well, including a characteristic of a touch and information relating to a plurality of touches.
According to one set of schemes for producing partially redundant sets of waves, a plurality of sets of waves are provided, each propagating at a different angle with respect to the axis along which a touch position is to be sensed. Each of the waves should be able to sense position along a significant portion of the axis. Thus, a traditional type touch system provides two sets of waves which are each parallel to an edge of a rectangular substrate and produce waves which propagate perpendicular to the edges. Thus, each set of waves is dedicated sensing a position along a particular axis. Likewise, a known bisected reflective array scheme overlaps waves over an insignificant portion of the touch sensitive surface, and the waves generated are of the same frequency, mode, axis of propagation and therefore are essentially fully redundant and likely bear essentially the same information.
The present invention also extends these same principles to encompass a number of other embodiments, including acoustic touch systems in which the acoustic waves travel along paths which are neither parallel nor perpendicular to an edge of a substrate or travel along a path which is neither parallel nor perpendicular to a reflective array. Thus, the present invention relaxes constraints imposed in prior touch position sensors through an understanding that the geometry of the touch sensor substrate, reflective arrays or acoustic paths need not limit the coordinate system represented in an output. Thus, the present invention may provide control systems which are capable of performing coordinate system transforms and higher levels of analysis of the information contained in the acoustic signals than prior systems.
In forming this understanding that a control need not be limited to a conversion of a characteristic timing of a perturbation of an acoustic wave into a coordinate position along a single axis, the possibility of non-Euclidean geometric shapes is developed. Thus, while the prior art teaches that acoustic touch sensing may be applied to spherical portions of CRT faceplates, the goal of the prior art was to provide a system in which analysis of the received acoustic signals were as if the substrate were planar. Therefore, those prior art systems were developed to compensate for the spherical aberrations in the design and placement of the reflective arrays. Likewise, a known prior art system employs a diverging set of waves incident on a reflective array to sense a unidirectional angular measurement. In this case, a control treats the unidimensional angular measurement as a single coordinate axis without transformation.
The present invention provides touch system flexibility allowing analysis of waves which propagate along non-orthogonal axes in the touch sensitive region of the touchscreen. Further, the present invention provides a touchscreen system which tolerates and analyzes waves which are overlapping in time, i.e., simultaneously impinging on one or more receiving transducers. Together, these related aspects of the invention provide greatly enhanced flexibility in the design of the touchscreen, with improved performance under adverse conditions.
The present invention also includes touch sensors for purposes other than graphic user interfaces. For example, applications in the field of robotics exist, in which it is desirable to endow robots with a sense of touch. While a number of sensor technologies exist, acoustic sensing provides an opportunity for a large area, high resolution, low cost per unit area sensor on a machine, for example, to detect contact or pressure with an adjacent object and to determine the location of the touch. Such machines often have nonplanar surfaces, and as such it is advantageous to provide a touch position and/or pressure sensor which conforms to the shell of the machine. According to the present invention, various surfaces having irregular geometries may be formed into sensor surfaces.
The present invention also provides a touch system allowing analysis of a wave perturbation of two different types of waves, the waves differing in mode, frequency, waveform, velocity, and/or wavelength. This system advantageously allows redundant position measurement and/or differential wave perturbation sensing.
One aspect of the invention can also be described as follows. Acoustic energy is emitted into a substrate supporting propagation of acoustic waves. This energy travels through a portion of the substrate to a receiving system, which may include redundant use of the acoustic energy emitting device. The energy is received as at least two distinct waves. These waves have differing paths or characteristic timing. These waves are non-orthogonal in either the time or space planes, meaning that they impinge simultaneously on one or more receiving transducers, or follow paths which are substantially non-orthogonal (having a relation different than 90xc2x0).
Therefore, one embodiment of the present invention, as depicted in FIG. 7, is somewhat similar to the xe2x80x9ctriple transitxe2x80x9d system, but allows acoustic signals following two different paths 1, 2 to be received simultaneously. This system provides a first path 2 with a single reflective array 5, which reflects acoustic waves off an opposite side 3 of the substrate 4, back through the touch sensitive region of the substrate, back into the reflective array 5, and to the originating transducer 6, with a maximum path length of about two times the sum of the height plus the width. The orthogonal axis receives a portion of the same acoustic wave from the transducer 6, which reflects off a diagonal corner reflector 7, along a perpendicular axis has a second reflective array 8. The wave is reflected as a set of waves 9 through the touch sensitive region of the substrate 4, and is incident on a third reflective array 10, which reflects the acoustic wave toward a second transducer 11 on an adjacent side of the substrate 4, near the first transducer 6. The maximum path length of this path is two times the sum of the height plus width. In this case, two transducers 6, 11 receive signals simultaneously for at least some delay times.
Another embodiment of the invention provides a sensor which employs a plurality of waves having differing frequencies, wavelengths, phase velocities, or amplitude. Such waves may also be non-orthogonal in the time or space planes, but need not be so. In other words, these distinguishable waves may travel sequentially and/or over orthogonal paths.
Where portions of acoustic waves are received simultaneously by a single transducer, it is generally preferred that a receiving circuit be sensitive to a phase of a received signal in order to help resolve interference effects. Likewise, where waves of differing frequencies are employed, it is preferred that the receiver selectively receive those waves according to their frequency. Where waves of differing wave propagation mode are employed, transducer having selectivity for differing waves modes may be provided. Therefore, embodiments of the present invention may also include a receiver sensitive to at least some wave characteristics.
A further embodiment of the invention provides a positive response sensor, e.g., one where an increase in received signal is representative of a typical perturbation. Typically, a perturbation in a positive response system will cause a change of some type in the wave, making it distinguishable from an unperturbed wave. Again, such a wave may be non-orthogonal in the time or space planes, but need not be so. For example, the unperturbed signal may be completely attenuated through filtering, and therefore not received by the receiver. In this case, only a single, positive response signal according to the present invention is received.
Thus, the present invention is not limited in the conventional manner to sequential receipt of independent coherent signals representative of waves propagating along Cartesian coordinate axes, and analysis thereof to determine an attenuation of a transmitted wave by a touch by detecting the energy of the wave with respect to time. In particular, according to the present invention, a plurality of waves may be received simultaneously, the received signal may be an incoherent superposition of components from different wave sets, the waves need not propagate parallel to a rectangular coordinate axis of a planar substrate, and detection is not necessarily based solely on a determination of a time of an attenuation in power of a received signal. An improved receiver is therefore employed which includes enhanced logical analysis of the received waveform. Advantageously the waveform sensitive analysis and enhanced logical analysis may be employed together.
The receipt of at least two distinct waves which overlap temporally may indicate two waves which each have substantial energy, each being specifically intended for receipt, and potentially bearing information relating to a touch position along a coordinate axis. Alternately, one of the two distinct waves may be due to unintentionally scattered waves, artifacts and interference that are not intended for use in touch detection. In either case, a touch-information carrying signal may be utilized even if superposed with other signal components.
The present invention allows receipt and analysis of partially redundant waves. Therefore, the effects of contamination and various artifacts may be reduced. Further, where differing wave modes or frequencies are used, a differential sensing approach may be followed to determine both position and a mode sensitive characteristic of a touch.
The present invention includes a system in which the position of a touch is determined by the controller independent of the physical axes of the substrate, thus providing for coordinate processing and transformation before output. This allows increased flexibility in the layout of the transducer systems. In this document, xe2x80x9ctransducer systemxe2x80x9d is defined to be the system that couples electronic signals to acoustic waves in the desired touch region including the transducer itself, e.g. a wedge or edge transducer, and associated reflective arrays if employed.
The present invention also allows receipt and analysis of signals which are excited by a common transducer representative of differing sets of wave paths with overlapping characteristic time-periods.
A still further aspect of the invention provides an acoustic wave touch sensor in which a touch is detected by a perturbation of a received signal where the perturbation may be a decrease in amplitude, an increase in amplitude, a change in phase of the received signal, or a combination of amplitude change and phase change.
One set of embodiments according to the present invention includes systems employing multiple waves sharing a common path portion. The known triple transit transducer also shares common path portions, but does not have simultaneously received waves or a transformation of coordinate system. In other words, the known triple transit system requires a time separation between received waves representing orthogonal axes, thus limiting the topology of the sensor.
According to one aspect of the present invention, a plurality of waves traveling along non-orthogonal axes in the active region of the touchsensor may have common path portions, being at least partially superposed. In particular, according to certain embodiments of the invention, these waves will share a common transducer, and a common axis of propagation from the transducer. The waves may differ, e.g., in path, mode, frequency, phase, propagation velocity, or wavelength. Therefore, some embodiments according to the present invention provide a reflective array which separates the waves to propagate along differing paths. Another set of embodiments provides a plurality of sets of distinguished reflective arrays, which reflect portions of the waves at differing angles or as waves of differing propagation modes, or both.
Sensor systems according to the present invention allow superposition of waves producing sets of touch-sensitive waves which are dispersed across the touch area of the substrate having characteristic time delays or other characteristics, and a system for receiving the dispersed waves and determining a characteristic of a touch or wave perturbation. The axes of propagation of one set of waves need not be orthogonal to those of another set. According to the present invention, these sets of non-orthogonal waves may be employed with orthogonal waves. By providing more than one set of these plurality of waves, a position of a touch may be determined using redundant information, e.g., having more information than is necessary to mathematically determine a position, allowing enhanced performance in the presence of noise, interference and shadowing.
As stated above, the acoustic waves may differ in other properties, including mode, propagation velocity, wavelength, which in general provides two advantages. First, waves having differing properties may have differing sensitivity to environmental conditions and artifacts. Thus, the differential effect on the sensing waves may be used to determine properties of an object in contact with the surface. Further, the differences in the waves may be used to selectively filter the waves, thus providing opportunity to selectively reduce noise or separate potentially interfering waveforms. Waves having differing wavelength in the substrate may be selectively redirected with reflective arrays having physical characteristics corresponding to that wavelength and its axis of propagation.
In another aspect of the invention, the coordinate system of a sensing wave is non-orthogonal with an output coordinate system. Therefore, a plurality of waves must be analyzed and their position information transformed in order to output a coordinate value. The plurality of waves may also be analyzed for redundancy to verify a touch coordinate, and potentially to resolve ambiguities, perhaps due to multiple touches, in the two dimensional position measurement.
In an embodiment of the invention, at least three distinct acoustic wave sets are excited, of which analysis of at least two are required in order to detect a two dimensional position of a touch. Therefore, under various circumstances, one or more waves may be ignored or unavailable, yet operation continues. Where at least three are available, the three waves may be analyzed for touch position consistency, artifact or interference, and to determine an optimum output indication of the position of the touch. The analysis of the at least three waves may also include an output of a plurality of simultaneous touch positions.
According to another embodiment, differing wave modes are induced in the substrate so that regions of low sensitivity employing one propagation mode correspond to regions which have adequate sensitivity employing a different propagation mode. For example, in regions where Rayleigh waves are heavily shadowed due to contamination, a less sensitive backup wave mode, e.g. a horizontally polarized shear mode, may be analyzed for this same region to determine touch data.
The dual mode operation allows operation with at least two waves, with spatial domain, frequency domain, wave propagation mode or time domain multiplexing. Therefore, signals may be received along differing paths, having differing frequencies, differing wave propagation modes, or differing locations of reception.
In order to provide waves having differing characteristics from substantially common sensor hardware, the signal from the transducer system may include a number of components. In order to provide frequency mode discrimination, the receiving system must distinguish between various received frequencies. With respect to a plurality of wave modes, either the differing wave modes must be converted to a single mode which excites the transducer, or the transducer must be sensitive to the various modes. With a time domain multiplexing system, readings according to various wave modes are taken sequentially. In order to detect spatially separated waves, a separate transducer may be provided or the waves may be redirected to a common receiving transducer. Where different types of waves are superposed, a perturbation will typically have a different characteristic time delay for the different waves, which is used to distinguish the particular wave.
Various embodiments of the invention analyze a potential ambiguity in the received waveform. That is, two waves, following different paths, arrive at the same receiving transducer within an indistinguishable time window, and thus a given wave perturbation is potentially attributable to either wave. Therefore, without further information, the controller might not determine, based on the signal of the received wave, which of the two possible paths the touch intersects. According to a subclass of these embodiments, however, a pair of such ambiguous signal perturbations occur. Thus, by analyzing the pair of ambiguous signal perturbations, with reference to a physical model of the sensor and additional information from signals from other wave sets, the position of the perturbation may be determined or predicted, and the ambiguity resolved. Further, as referred to herein, the position may be sensed unambiguously by a pair of acoustic waves emitted along a single set of superposed arrays.
According to another aspect of the invention, additional information may be obtained from an additional set of superposed arrays, e.g., along another axis. This information may be further employed in determination of the coordinate position. More generally, the present invention encompasses the superposition of reflective arrays, e.g., to scatter a plurality of waves coherently, and a physically superposed array structure.
Where the waves travel along different paths, often the waves will be directed towards different edges of the substrate. Therefore, for example, two waves may be sensed with two different receiving transducers simultaneously. Advantageously, therefore, a traditional touchscreen system and a touchscreen system with inclined propagation paths are superposed. Embodiments according to the present invention may thus provide multiple channels for receiving acoustic wave information.
Reliability of operation is enhanced according to the present invention even where different types of touching objects are to be sensed, such as fingers, gloved fingers, styli, etc. Likewise, potentially interfering factors may be identified and/or filtered or ignored.
By allowing multiple wave modes and/or paths, the advantages of partially redundant measurements and differential wave perturbation characteristic sensing are realized.
Algorithms may use redundant coordinate information to verify and perhaps resolve ambiguities in two-dimensional position measurements.
Alternately, algorithms may support systems with redundant coordinate measurements in which only two of three or more sets of waves are needed to reconstruct two-dimensional coordinates of a touch.
Systems according to the present invention also encompass multiple user touch applications. In such cases, the redundancy of the multiple wave paths may be used to resolve multiple degrees of freedom. For example, such multiple user touch systems might include a classroom multi-media device that is simultaneously hands-on for the teacher and several students, interactive museum displays, a two-person video game with a touch interface, or a large table-top display of engineering drawings that can be simultaneously reviewed and edited by a small group of engineers. Complex control system human interfaces are also possible.
A multiple-user touch/display system will typically require a larger display device than a system intended for one user at a time, such as is possible with projection systems and large flat panel displays commercially available or under development. Therefore, various methods according to the present invention allow sensing of multiple touches, reduction of acoustic path lengths and of likely sources of interference. Embodiments according to the present invention also employ aspects which allow longer acoustic path lengths.
Simultaneous touches are problematic for existing touchscreen products. Analog resistive, capacitive, and force-sensing touch technologies inherently confound a multiple touch with a false touch at an intermediate position. High-resolution resistive and capacitive touch schemes that cover larger areas with discrete touch zones become awkward and expensive due to the large number of electronic channels required. If means are provided to resolve discrete ambiguities, acoustic touch technologies have the inherent capability to recognize simultaneous multiple touches. In addition to true multiple user applications, a simultaneous touch capability would also enable touch applications in which a single user simultaneously touches with both hands or more than one finger in one hand. For example, a virtual piano keyboard on a touch/display device that supports playing of chords.
It is therefore an object of the invention to provide a system in which waves of differing characteristics are used to sense a touch in a substrate, wherein the waves may have differing, non-orthogonal axes of propagation, differing wave propagation mode, differing frequency, wavelength or phase velocity.
It is another object according to the present invention to provide a touch sensor comprising an acoustic wave transmissive medium having a surface and a touch sensitive portion of said surface; a transducer system for emitting acoustic energy into said medium; and a receiver system for receiving the acoustic energy from the substrate, for determining a perturbation of said acoustic energy due to a touch on said surface, said touch sensor comprising a reflective array having a plurality of spaced elements for scattering portions of an incident acoustic wave as waves having a different propagation vector than said incident wave and passing other portions unscattered, said array being provided an array selected from the group consisting of:
(a) an array associated with said medium situated along a path, said path not being a linear segment parallel to a coordinate axis of a substrate in a Cartesian space, a segment parallel to an axial axis or perpendicular to a radial axis of a substrate in a Cylindrical space, nor parallel and adjacent to a side of a rectangular region of a small solid angle section of a sphere;
(b) an array situated along a path substantially not corresponding to a desired coordinate axis of a touch position output signal;
(c) an array situated along a path substantially non-parallel to an edge of said medium;
(d) has a spacing of elements in said array which differs, over at least one portion thereof, from an integral multiple of a wavelength of an incident acoustic wave;
(e) has elements in said array which are non-parallel;
(f) has an angle of acceptance of acoustic waves which varies over regions of said array;
(g) coherently scatters at least two distinguishable acoustic waves which are received by said receiving system; and
(h) combinations and subcombinations of the above,
except that said array in (d), (e) or (f) is not provided parallel and adjacent to a side of a rectangular region of a small solid angle section of a sphere.
It is also an object according to the present invention to provide a controller which is capable of logically analyzing two sets of waves derived from a common transmit transducer burst which are received simultaneously, i.e., in which the wave being received may not be distinguished solely by reference to a time window. Thus, the system need not maintain a time separation between a plurality of waves for proper operation.
It is a still further object of the invention to provide a receiver in which a received signal is analyzed for waveform information, due e.g., to multipath signal paths. Further, the receiver according to the present invention may analyze the received signal for a touch indicated by a perturbation of complex amplitude rather than merely an attenuation in received power.
A further object according to the present invention is to allow output of a coordinate position in an output coordinate system, typically Cartesian, of a perturbation of acoustic waves, each of which measures a coordinate substantially different from the axes of the output coordinate system.
Thus, touch position sensors according to the present invention may provide some or all of the following advantages:
(a) Tolerance to shadowing effects of contaminants by obtaining redundant information and/or employing robust waveforms.
(b) A higher signal to noise ratio due to availability of redundant coordinate information.
(c) A multiple wave mode sensor allowing the composite advantages of each selected type of wave mode, e.g., high sensitivity to touch for Rayleigh wave modes, relative immunity to contaminants for horizontally polarized shear modes.
(d) Ability to detect a mode sensitive perturbing characteristic of a touch based on differential wave perturbation and/or appearance of a characteristic new signal.
(e) Versatility in the selection of substrate, e.g., use of larger sizes, non-rectangular shapes, large solid angle sections of spheres and other non-planar topologies.
(f) Ability to reliably reconstruct multiple touches and hence support applications in which more than one finger, hand, or user may simultaneously input touch information.
These and other objects will become apparent from a review of the drawings and Detailed Description of the Preferred Embodiments.